Fluorine doping for improved thermoelectric properties of spark plasma sintered bismuth telluride

Bismuth-telluride(Bi2Te3) is considered to have the best thermoelectric properties at room temperature(ca.300 K).Thus,synthesis and improvement of Bi2Te3and its derivatives quickly and cost-effectively at favorite temperatures are of interests.Recently,doping fluorine(F) into electronic materials(e.g.,FTO) has gained attention;however,it is not applied to Bi2Te3till now.Here,our synthesis of F-doped Bi2Te3for thermoelectric application is introduced using spark plasma sintering(SPS) for Bi2Te3preparation and reactive ion etching(RIE,with SF6gas) for F-doping.The exposure time of SF6plasma is adjusted to evaluate F-doping effect on the thermoelectric properties of the samples.During characterizations,the increased electrical conductivity and the improved Seebeck coefficient of F-doped Bi2Te3are observed.Through spectroscopic studies and DFT calculations,the main mechanism behind that improvement is unveiled.It also emphasizes the essential role of the F-doping(optimum treatment time of 40 s) in increasing the carrier concentrations as well as electrical conductivity.With increasing measurement temperature(300-510 K),F-doping raises the figure of merit of electron rich Bi2Te3from 1.0 to 1.11(peaked at 390 K).